Preparation of formcoke



Jan. 23, 1962 K. BAUM ETAL PREPARATION OF FORMCOKE 4 Sheets-Sheet 1Filed Jan. 22, 1957 ZOZ Jan. 23', 1962 K. BAUM lETAL PREPARATION OFFORMCOKE 4 Sheets-Sheet 2 Filed Jan. 22, 1957 N mDoE KURT BAUM ROBERT J.FRIEDRICH Jan. 23, y1962 K.BAUM ETAL PREPARATION OF' FORMCOKE 4Sheets-Sheet 3 Filed Jan. 22, 1957 .m .mm-DDE mxOoEmOm KURT BAUM ROBERTJ. FRIEDRICH 4 Sheets-Sheet 4 Filed Jan. 22, 1957 .v mnw KURT BAUMROBERT J. FRIEDRICH 3,018,227 PREPARATION F FORMCOKE Kurt Baum, Essen,Germany, and Robert J. Friedrich,

Library, Pa., assignors to Consolidation Coal Company, a corporation ofPennsylsania Filed Jan. 22, 1957, Ser. No. 635,421 11 Claims. (Cl.202-26) The present invention relates to formcoke and a method ofpreparing it. More particularly, the present invention is directed to acomposition of matter useful as a metallurgical fuel and the method ofpreparing it.

At the present time virtually the exclusive metallurgical fuel is cokewhich has been prepared from caking coal in by-product coke ovens orbeehive coke ovens.

By-product coke ovens require an initial high capital investment, resultin high processing costs because of the inherent batch-Wise processingand impose rather severe limitations on the nature of the coal feedmaterial. Beehive coke ovens similarly have high processing costsbecause of the batch-wise nature of the treatment and do not produce anyvaluable by-products.

Another disadvantage of current techniques for making coke is the rathersubstantial loss of useful solid coke product resulting fromfragmentation which occurs when the coke product is discharged fro-m theoven whether of the beehive or by-product variety. For mostmetallurgical applications, only the large fragments of coke aremarketable. It is possible, of course, to recycle into the coke oven aportion of the coke breeze resulting from fragmentation. A substantialportion of the product coke, however, is not saleable as a premiumproduct because of the size requirements of the coke market.

According to the present invention, we have discovered a method forpreparing a metallurgical fuel which has the desirable intrinsicproperties of conventional coke with the following additionaladvantages: (l) the material is produced in a continuous orsemi-continuous manner rather than in a batch process; (2) the productpossesses substantially uniform size and configuration; (3) the overallyield of valuable liquid by-products is significantly greater than thatobtained in conventional by-product coking; (4) the processing timerequired is significantly less than that required in conventional cokemaking processes; and (5) the process may be applied to any of thecaking bituminous coals without regard to the swelling pressures whichsuch coals would exhibit during conventional coking.

Essentially the formcoke of the present invention is prepared from aformulation comprising at least three ingredients which include (a) acaking bituminous coal; (b) a low temperature carbonization char whichhas been obtained by iluidized low temperature carbonization of a highvolatile bituminous coal; and (c) a pitch binder obtained by pyrolytictreatment of carbonaceous solid fuels, at least a portion of which has afixed carbon content exceeding 25 percent. The formulation has avolatile matter content greater than 22 percent. The mixture of startingmaterials is blended, kneaded, and briqueted under pressure into uniformshapes. The briquets possess a satisfactory raw strength which isnecessary to permit their handling and movement into coking apparatus.The resulting briquets are shock heated to a temperature above theplastic range of the caking coal constituent to effect virtuallyinstantaneous coking of the outer shell of the briquet, and are retainedat a temperature of 900 to 1250 F. until the entire briquet mass haspassed through the plastic temperature range of the caking coal and hasachieved a temperature above 900 F. Thereafter the coked briquets arecalcined by continued heating to a temperature suicient for reducing thevolatile matter content to an acceptable value. The calcined briquetsted States Patent O ,Mice

thereupon are cooled to a temperature below their atmospheric kindlingtemperature and are recovered as a useful fuel for metallurgicalpurposes.

The formcoke produced by the present invention has dimensionally uniformstructure, has a homogeneous cornposition, is highly porous, and has anapparent density equivalent to that of existing metallurgical coke. Onmicroscopic inspection our new formcoke is virtually indistinguishablefrom existing strong metallurgical coke since the individual particlescomprising the formulation completely lose their discrete identityduring processing. The tumbler strength of our new formcoke is as highas that of existing strong metallurgical coke. Sulfur content andvolatile matter content correspond to that of coke prepared from thesame starting coal or coal blend.

We are aware that many prior investigators have proposed that coke-likematerials be prepared in definite shapes by briqueting and subsequentcoking and calcination. Such calcined briquets, however, have been ofpoor quality because of non-homogeneity, high density and low strength.The individual particles which were Vabout 20 to 25 pounds per cubicfoot.

agglomerated .during prior art briquet preparation are only looselybound in the calcined briquets. The discrete, loosely bound particlescould be readily abraded from the calcined briquets. The weak bondingpermitted l substantial shattering tooccur when the calcined briquetswere subjected to mechanical stresses. Another defect of prior artcalcined briquets, especially those produced from coal alone, was thedistortion of shape and resultant cracks and fissures which occurredduring the calcining and cooling stages. Prior art calcined briquetspossess too high a density and too low a strength.

The formcoke of the present invention has substantially uniformundistorted shape; it is free from cracks and fissures; it appears topossess a homogeneous composition similar to that of premiummetallurgical coke produced in coke ovens from good caking coals. Theparticulate starting materials are securely bound in and be` come partof a continuum of carbonaceous material whereby their initial characteras discrete particulate ingredients is lost.

I. BRIQUET FEED FORMATION A. F liudized low temperature carbonizationchar.-One

of about 800 to about 0 F., volatile material is4 evolved in the form ofgas and tar. The quantity of valuable liquid tar recoverable via lowtemperature carbonization is from about l5 to about 40 gallons per tonof coal in contrast to the yield of about Sto l0 gallons per ton of coalrealized in by-product coke ovens. The solid residue remaining afterevolution of volatile matter is Itermed chan The physical nature of thechar is dependent upon the mechanical conditions of carbonization. Manylow temperature carbonization processes known to the art will producechar having a bulk density of 30 pounds per cubic foot and higher. Forour formcoke, the char must have a sponge-like porous composition and adensity of less than 30 pounds per cubic foot.

To prepare our new formcoke, the char component must be produced by lowtemperature carbonization conducted under fluidized solids contactingconditions. When produced in fluidized low temperature carbonizationprocesses, the char is swelled and expanded into uify, rounded solidparticles. The sponge-like porous properties of the char particlesresult in a low bulk density of the material and a correspondingly lowphysical strength. The bulk density of the material is from The charresulting from fluidized low temperature carbonization,

moreover, is in discrete particulate form, -for example,

capable of passing through a 14 mesh Tyler standard screen. Y

It is possible to produce high density char from high volatilebituminous coal by fluidized low temperature carbonizaton process whenthe untreated coal is introduced directly into the iluidizedcarbonization stage and its operability (i.e., its ability to retainparticulate configuration and avoid agglomeration) is forced by means ofmechanical stirring devices. Such dense chars are not suited to thepreparation of our formcoke. The uidized low temperature carbonizationprocess required for the fiuidized low temperature carbonization char isone in which the coal achieves operability by virtue of preliminarytreatments such as preoxidation, for example.

Throughout this specification, the abbreviation LTC refers to lowtemperature carbonization; the phrase fluidized LTC char refers to thesolid particulate residue resulting from a low temperature carbonizationofV high volatile bituminous coal conducted under fluidized solidscontacting techniques.

'I'he final carbonizing temperature determines to alarge extent theultimate volatile material content of the char particles. For purposesof the present invention the carbonization temperature should not exceed1350 F. 'If the char is to be thermally treated prior to briquetblending according to our invention, such thermal treatment should notbe carried out at ternperatures above 1350 F. PreliminaryV treatment atexcessive temperatures tends to graphitize the char, to destroy itsporous character, increase its density and thereby to render it lessdesirable for formcoke preparation.

Low temperature carbonization char which has been prepared fromprocesses which are not conducted under fluidized solids contactingconditions are unsuitable for preparing our new form'coke. These charsgenerally have a higher bulk density than fluidized LTC chars and do notpossess the uffy, sponge-like composition we have found to be necessary.

The high volatile coal employed in preparing the fluidized LTC char neednot be one normally considered as a caking coal. By that We mean thatthe char may be prepared from high volatile coal which would not exhibitsatisfactory caking properties for metallurgical coke ovens. In manyareas of the world such coal is readily available. Such coal, now has noutility in the preparation of metallurgical fuels, although it may beconverted into a lluidized LTC char quite readily and be used in thatform as a major constituent in the preparation of metallurgical fuelsaccording to our present invention.

Fluidized LTC char comprises about 45 to 80 percent by weight of thebriquet formulation.

`B. Cakng bituminous cal.-The caking bituminous coal employed in thebriquet formulation has a volatile matter content exceeding about 30percent by weight. Such coals are described as high volatile cakingbituminous coals. Preferably, the caking bituminous coal is crushed to asize consist approximating that the fluidized LTC char. For example,high volatile caking bituminous coal ground to pass through a 28 meshTyler standard screen has been found quite satisfactory in preparingformcoke according to this invention. Where the coal is too finelyground, the resulting excess surface area introduces difficultiesrelated to the pitch binder required for our new process. A small amountof residual moisture is not detrimental in the present process althoughexcessive moisture is undesirable. Generally, coal which has been storedin open atmosphere acquires an equilibrium moisture content of about to8 percent by weight which is satisfactory. If desired, the cakingbituminous coal employed in the briquet formulation may be the samecaking bituminous coal used as the feed material for the fluidized lowtemperature carbonization process which supplies the char for thebriquet various coals provided the blend has sufficient cakingproperties and volatile matter content.

The briquet formulation from this invention comprises abolut 10 to 35percent by weight of caking bituminous CO3 C. Pitch binden-*The briquetformulation according to this invention comprises about 6 to 20 weightpercent of pitch obtained by pyrolysis of caking coals. The pitch shouldbe free of materials boiling below about 350 C. and may additionally be`free of materials boiling below 400 C.V if desired. The melting pointof the pitch should be below about C.V A ring and ball melting point ofabout 60 to 90 C. is satisfactory, (ASTM: E28-42T).

From about l to 12 weight percent of the briquet formulation shouldcomprise a high carbon pitch having a fixed carbon content exceeding 25percent. A pitch meeting these requirements can be obtained by thermaltreatment of pitches at temperatures exceeding about 1500 F. An exampleof such a pitch would be the pitch obtained from high temperaturecarbonization of coal in a conventional coke oven or, more conveniently,it may be the pitch which is produced during the calcining of thebriquets according to this invention.

Up to about 15 weight percent of the briquet formulation may comprise alow carbon pitch having a fixed carbon content of less than about 20percent. Generally pitches which have not been exposed to thermaltreatment at temperatures above 1400 F. are suitable. The pitch normallyobtained from low temperature carbonization of caking bituminous coalmeets these specifications. Fixed carbon content of pitches isdetermined by the technique employed in determining fixed carbon contentof coals (ASTM: D27l-48, paragraph 16).

The pitch binder serves two functions in our invention. First, the pitchserves as an adhesive to bind the particles of caking coal and uidizedLTC char Vinto shaped briquets. In this function the pitch must coat thesurfaces of the particles in the raw briquet feed.

Second, the pitch serves as a flux in the thermal treating stage of theprocess to cause the components of the briquet to fuse together into ahomogeneous mass. With proper fluxing action, the individual solidparticulate constituents become securely bound in the product formcoke.The resulting formcoke product, like existing metallurgical coke of goodquality, is relatively free of non-homogeneity.

The described high carbon pitch alone may serve both functions of thepitch binder. In fact, excellent formcoke may be prepared according tothis invention from our briquet formulation wherein about 10 to l2Weight percent of high carbon pitch is employed as the exclusive pitchbinder. However, We prefer to provide an intetegrated self-sustainingformcoking process which employs the high carbon recycle pitch,autogenously obtained from the briquet coking and calcining stages, as'the high carbon pitch component of the briquet formulation. We havefound that the quantity of high carbon pitch which may be recovered inthis manner is sufficient to supply only up to about 6.5 percent byweight of fresh briquets under continuous processing conditions. Thisquantity of pitch is insufficient to serve the adhesive function ofpitch binder, although it is adequate to serve the fluxing function.Additional high carbon pitch for the adhesive function may be obtainedfrom extrinsic sources such as conventional coke oven processors or maybe prepared by thermal treatments of low carbon pitch to supply therecycle deficiency inherent in continuous processing. Where additionalhigh carbon pitch for the adhesive function may be obtained fromextrinsic sources such as conventional coke oven processors or may bepreing. Where additional high carbon pitch is obtained 5 extrinsically,the incremental quantity need be only l to 3 percent of the weight ofthe raw briquets.

As an alternative, however, a low carbon pitch may be employed to makeup the intrinsic deficiency of recycle pitch. Low carbon pitch isreadily available in the LTC tar which is obtained contemporaneouslywith the uidized LTC char. The presence of finely divided particles ofcoal and partially devolatilized coal in pitches obtained from uidizedlow temperature carbonization does not adversely affect their utility inthe present invention. The low carbon pitch adequately serves theadhesive function of the pitch binder and does not interfere with thefluxing function provided by the high carbon pitch. Low carbon pitchalone is less effective for the fluxing function and also is of doubtfulvalue alone for the adhesive function. Briquets formed from low carbonpitch alone tend to exhibit shape distortion and are readily deformable.Where low carbon pitch is employed as the incremental pitch, greaterquantities are required than where high carbon pitch is selected as theincremental pitch. Up to about l5 percent by weight of LTC pitch may beemployed in the briquets. In general, one incremental percent of highcarbon pitch is about as effective in our invention as three incrementalpercent of low carbon pitch.

It is possible to convert low carbon pitches into high carbon pitches byselected thermal treatments. Such processes are beyond the scope of thepresent invention except for the following caveat. Simple thermaltreatment of a low carbon pitch, while effective in increasing the fixedcarbon content, also results in a significantly increased melting pointof the treated pitch. The melting point of the entire pitch which isemployed in our invention should be, as previously stated, from about 60to 90 C. as measured by ring and ball determination.

D. Recycle coke.-Abrasion of the formcoke product obtained in thepresent process results in the production of only a small quantity ofundersized coke particles. We have been able to recover all of theundersized coke particles for reblending with the briquet formulation.Generally the amount of recycle coke, which preferably is crushed topass through a 28 mesh Tyler standard screen, will be about 5 percent ofthe briquet formulation. Unlike the other ingredients of our briquetformulation, these recycle coke particles retain their particulateidentity in our process and are identifiable in the product formcolce.The recycle coke particles, however, are cornpletely surrounded with acontinuum of homogeneous coke and do not adversely affect the formcokeproperties. Up to about 8 percent by weight of crushed formcokefragments may be added to the formulation without serious difficulty.

E. Preferred embodz'mentf-We have found that the following formulationWill produce satisfactory formcoke according to this invention.

Table I BRIQUET FORMULATION Constituent Weight Percent Fluidized lowtemperature carbonization cha 58. 5 High volatile caking bituminouscoal... 25. 0 Low temperature carbonization pitch.. 5. 3 Pitch recoveredfrom process 6.2 Recycle cnice 5.0

. 6 for example, to pass through a 200 mesh Tyler standard screen. Thecomminuted solid pitch is thereupon uniformly mixed with the iluidizedLTC char and caking coal.

The blended formulation has a volatile matter content greater than 22percent, preferably from about 24 to 30 percent by weight. (ASTM:D27148, paragraph 13a and 14a.)

G. Kneading.-Following the blending of ingredients, the formulationshould be kneaded for a brief period in accordance with the well-knownbriqueting art. The kneading operation usually is carried out in a tankhaving agitation paddles rotatable in horizontal planes. Live steam isusually passed through the briquet formulation in the kneadingapparatus. The function of the kneading operation is to causeemulsification of the pitch binder to assure that the binder becomesuniformly spread over the surfaces of the particles. Thus kneading iscarried out at a temperature above the melting point of the pitch. Wehave found that from about 7 to 10 minutes residence time in a steamkneader is satisfactory for our present process.

The kneadedv raw briquet mixture preferably should be passed quicklyfrom the kneading apparatus into briqueting apparatus.

mediately above the briqueting apparatus.

H. Briqueting.-The briqueting stage of the present` process preferablyshould be conducted at a temperature of about 25 to 40 F. above themelting point ofthe pitch employed in the briquet formulation. Theapplication of live steam in the briqueting stage is a preferred methodof supplying necessary heat. Thus the preferred briqueting temperatureis about 200 F., a value readily attainable with inexpensive steam. Anywell-known briqueting apparatus is suitable for the briqueting stage. Weprefer to use roll presses.

We have found that the kneaded briquet formulation must be pressure-fedinto such roll presses. Pressure feeding is required to assure that thepockets of the roll press be filled completely with briquet formulation.Cornpression pressure of 3000-5000 p.s.i.g. during actu-al briquetformulation has been found satisfactory.

Any desired geometric shape is satisfactory for the briquets. Ovoids,pillow blocks and cylinders have been found suitable. We have beensuccessful in preparing formcoke from briquets having dimensions up totwo inches and more. We prefer to employ briquet sizes such that eachparticle within the briquet is not more than about one inch from thenearest outer surface of the briquet.

The briquets leave the briqueting press at a temperature slightly abovethe melting point of the pitch. In this condiiton, they are somewhatpasty and Vare deformable. Severe mechanical shock will cause shapedistortion of briquets in this condition. lf the briquets are allowed tocool to a temperature very slightly above the melting point of thepitch, a maximum mechanical shock resistance results. The briquetsurface becomes hardened to resist deformation, yet the interior of thebriquet remains resilient to resist fracture during handling. If thebriquets are allowed to cool below the melting point of the pitch, theybecome brittle and susceptible to fracture. Accordingnly, we prefer totransport the briquets for further processing at a temperature of about70 to 80 C. We have found that the briquets will possess a maximum rawstrength during the period occurring from labout 2 to about l0 minutesfollowing exposure to atmospheric temperature upon discharge from thebriqueting apparatus. Accordingly, we prefer that the briquets behandled with gentleness to avoid deformation during the first twominutes or so after formation. Transportation and mechanical handling ofthe briquets should occur within the succeeding few minutes to avoidfractures and deformation.

In most briqueting plants, this is not a problem since the steam kneaderusually is installed im-4 Any undersize fragments of briquets may becollected and returned to the blending stage for recombination in Y theraw briquet feed mixture.

I. Shock hearing-The briquets formed as described should be subjected toa shock heating treatment which virtually instantaneously raises theirtemperature above the plastic range of the caking coal. Preferably thebriquets should be heated so that the outer surface of the briquet isvirtually instantaneously elevated above the plastic temperature, i.e.,to a temperature in the range of labout 900 to 1250 F. The inner portionof the briquet will attain the shock heating temperature somewhat moreslowly.

The rapid heating of the outer shell of each briquet serves to form acrust of coke which is sufficiently strong to retain the form and shapeof the briquet while the interior portions pass through the plasticrange of temperature. When each briquet possesses a crust of coke, thereis no tendency for individual briquets to fuse together since the cokedsurface is non-cohesive.

As the briquets pass through the coking stage, the thermal treatmentcauses evolution of volatile material from the briquet constituents inthe form of gases and tars which can be recovered as valuableby-products. The evolved products escape from the briquets and yarecarried away in a vapor phase for recovery. The high boiling volatileconstituents can be recovered as the recycle pitch required in thebriquet formulation. In a preferred formcoking process, these volatilematerials are exposed to temperature in excess of about l550 F. prior torecovery to assure that the resultant pitch will be of the describedhigh carbon type required in our briquet formulation.

Rapid heating through the plastic range is desirable from an economicstandpoint since the briquets are thereby maintained under processingconditions for only a brief period of time in contrast to coke oventreatment, for example. However economic considerations are not the onlycriterion determining the shock heating rate. We have found that theplasticity of caking coals varies considerably according to the heatingregime to which they are exposed. Where a caking coal is heated rapidlythrough its plastic range, its fluidity is greatly increased over thatexhibited when heated slowly through its plastic range. This increasedfluidity resulting from shock heating serves in our invention to producea melted briquet mass in which the iluidized LTC char is engulfed byliquid coal. The succeeding coking of the coal forms a carbonaceouscontinuum in which the discrete particulate starting materials aresecurely bound as a homogeneous material.

The briquets should be retained under shock heating conditions at atemperature of about 900-1250 F. for sulicient time to permit thebriquets to pass entirely through the plastic range and achieve atemperature above 900 F. throughout. Where small briquet shapes areemployed, the retention time will not be great. When larger briquetshapes are desired, the retention time may be appreciable. A residencetime of about 30 minutes at about 1100 F. has been found satisfactory inproducing briquets of about 2-inch diameter. Attempts to subject theshock heated briquets to `a further heat treatment at highertemperatures before the entire mass has passed through the plastictemperature will cause severe fracturing of the briquets.

The shock heating may be effected in a variety of ways. One technique isto pass a hot inert gas at yabout 2200 F. through a downwardly movingbed of the briquets. Alternatively the briquets may be plunged into alluidized bed of nely divided inert solid particles maintained at thedesired shock heating temperature.

J. CaIcining.-When the briquets have been heated throughout to atemperature above 900 F., they can be further heated to a naltemperature above about 1550 F. Heating rates above about 50 F. perminute should be avoided. A heating rate of about 20 to 35 F. per minuteis preferred. The nal temperature determines to a large extent thequantity of volatile matter remaining in the coke. The volatile materialevolved from the coked briquets may be recovered in the vapor phasetogether with the volatile materials evolved from the shock heatingstage.

K. Cooling-When the coked briquets have attained the desired calciningtemperature, they should be gradually cooled to a temperature below theatmospheric kindling temperature of the formcoke. Cooling rates up toabout 30 to 35 F. per minute have been found satisfactory. Excessivecooling rates, c g., 60 F. per minute, will introduce cracks andfissures in the product formcoke. We have found that the passage ofrelatively cool inert gases, e.g., flue gases at about 400 F., through amoving bed of formcoke will effect the desired cooling to a formcokedischarge temperature of Vabout 600 F.

L. Formcoke properties-The formcoke produced by our invention isvirtually indistinguishable from metallurgical coke obtained fromby-product coke ovens, except that our new formcoke has the definiteadvantage of uniform size and shape. Table II lists some of theproperties of our new formcoke.

Table II PHYSICAL PROPERTIES OF FORMCOKE AND EXISTING METALLURGICALCOKES lRauge reported for 12 U.S. coke plants, Contribution To TheMetallurgv cf Steel Number 43, Coke Evaluation Project, American Ironand Steel Institute, New York, 1953.

For a full understanding of the present invention, its object andadvantages, reference should be had to the following description andaccompanying drawing in which:

FIGURE l is a schematic ilow diagram illustrating apparatus adapted foruse preparing formcoke according to this invention;

FIGURE 2 includes a photograph of coke oven coke as recovered from aby-product oven and four photomicrographs (15 power magnification) andthree photomicrographs (3 power magnification) of thin sections of thecoke;

FIGURE 3 includes a photograph of typical calcined formcoke preparedaccording to our invention together with a photograph of split formcoke,two photomicrographs (15 power magnication) and one photomicrograph (3power magnification) of thin sections of the formcoke; and

FIGURE 4 includes three photomicrographs (3 power magnification) of lowstrength metallurgical coke, high strength metallurgical coke andtypical formcoke prepared according to our invention together with twophotomicrographs (l5 power magnification) of each of the identifiedmaterials.

Formcoke suitable for use as a metallurgical fuel may be prepared fromcaking bituminous coal in a continuous manner according to the owdiagram illustrated in FIG- URE 1.

The present process employs as starting material (a) a high volatilebituminous coal 10 which need not possess caking properties satisfactoryfor use as a metallurgical coke oven feed material and (b) a highvolatile caking bituminous coal 11. Where high volatile caking coal isreadily avaliable, it may be used exclusively.

High volatile bituminous coal is subjected to fluidized low temperaturecarbonization in a processing stage 12. The tar and gas products of lowtemperature carbonization are recovered through a conduit 14 forrefining in a tar recovery stage 16. The product char from the fluidizedlow temperature carbonization stage 12 is introduced through a conduit18 into a briquet blending stage 20. High volatile caking bituminouscoal 11 is introduced directly without thermal treatment into theblending stage 20 through a conduit 22. The pitch obtained from lowtemperature carbonization may be withdrawn from the tar recovery stage16 through a conduit 24 and employed as the low carbon pitch of thebriquet formulation. High carbon pitch is introduced into the briquetblending stage 20 through a conduit 26.

The raw briquet mixture is homogeneously mixed in the blending stage 20and transferred to a kneading stage 28. The kneaded, blended raw briquetmixture is transferred to a briqueting stage 30 which employs forcedfeeding apparatus (schematically indicated) 32 to assure that thebriquet forming pockets are substantially filled with raw mixture.

VProduct briquets are recovered from the briqueting stage 30 and passedover a screen 34 through which briquet fragments may be recovered forrecycle in the r'aw briquet blending stage 20 through a conduit 36. Theintegral briquets are transferred by conveying means 38, preferablyduring the period 2 to 10 minutes after leaving the briqueting press 30to a thermal treatment vessel 40.

The thermal treatment vessel 40 comprises three separated zonesincluding an upper shock heating zone 42, a center calcining zone 44,and a lower cooling zone 46. Hot inert gases are introduced into theshock heating zone 42 through a conduit 48 and into the calcining zone44 through a conduit 50. The hot gases introduced through conduits 48and 50 supply the heat required for the thermal processing. Relativelycool gases are recovered through a conduit 52 between the shock heatingzone 42 and the calcining zone 44. Evolved gases and tars are carriedwith the spent heating gases to a condenser 54. Readily condensible taris recovered from the bottom of the condenser 54 through a conduit S6and flashed in a distillation zone 58. The high boiling portion of therecovered tars is recovered from the distillation zone 58 through aconduit 26 for use as the high carbon pitch in the briquet formulation.The lower boiling liquid tar constituents are recovered as distillatesthrough a conduit 60 and may be combined with the LTC tar for recoveryof valuable liquid products. Non-condensible gases exiting from thethermal treatment vessel 40 through the conduit 52 are eliminated fromthe condenser 54 through a conduit 62.

The briquets entering the shock heating zone 42 are rapidly heated ontheir surface through the plastic temperature 'of the caking coal whichthey contain. The briquets are retained in the shock heating zone 42until the briquets attain throughout a temperature in excess of 900 F.

The briquets at a temperature of 900 to l250 F. pass downwardly as amoving bed from the shock heating zone 42 into the calcining zone 44where they are gradually further heated to a calcining temperature abovel550 F. The calcined briquets pass downwardly as a moving bed into thecooling zone 46 and are discharged from the bottom thereof at atemperature below the atmospheric kindling temperature of the briquet.Cool inert gases are introduced into the cooling zone 46 through aconduit 64. The heated gases are recovered from the cooling zone 46through a conduit 66. The gases emanating through the conduit 66 may beemployed in a heat exchange 68 for generating low pressure steam whichmight be used, for example, in the kneading stage 22'5.

A"Product formcoke is discharged from the cooling zone 10 46 onto ascreen 70 through which formcoke fragments can pass for return through aconduit 72 to be recombined in the raw briquet blend. The intact productformcoke is recovered from the screen 70 for use as a metallurgicalfuel.

The time required to prepare formcoke after the briquets have beenformed is about two hours, including the shock heating, calcining andcooling stages. The product has properties comparable to metallurgicalcoke which requires about eighteen hours processing time in v typicalby-product coke ovens.

The properties of the formcoke produced by our invention can beillustrated by the petrographic photomicrographs and photographspresented in FIGURES 2 through 4.

FIGURE 2(A) is a photograph of a complete fragment o-f coke obtainedfrom a by-product coke oven. The complete fragment of coke in FIGURE2(A) comprises the cauliflower end (a), the dense, good metallurgicalcoke (b), and the weak, friable envelope coke (c). FIGURE 2(B) is aphotomicrograph taken at 3 power magnification of a thin section ofenvelope coke. FIGURE 2(G) is a photomicrograph taken at 3 powermagnification of a thin section of the dense good coke. FIGURE 2(D) is aphotomicrograph taken at 3 power magnification of a thin section of cokefrom the cauliflower end of the coke fragment. FIGURE 2(B) is aphotomicrograph taken at 15 power magnification of a thin section ofenvelope coke. FIGURE 2(F) is a photomicrograph taken at 15 powermagnification of a thin section of the dense good coke. FIGURES 2(G) and2(H) are photomicrographs taken at 15 power magnification of two thinsections of the cauliflower end of the coke fragment.

FIGURE 2(A) is representative of the coke product resulting from theconventional by-product coke ovens. When this coke is transported andused in metallurgical operations, the principal shatter, breakage andloss of product results from the relatively weak coke which occurs atthe cauliflower end and at the envelope end of each coke fragment. Thegood, strong coke which is produced between the cauliflower and theenvelope is the desirable product which possesses a relativelyhornogeneous texture and a relatively thick cell wall structure.

Throughout FIGURES 2(B) and 2(H), the black areas of thephotomicrographs indicate coke material and the white or gray areasindicate void spaces or cells. The friability of envelope coke isapparent from viewing FIG- URE 2(B) which indicates the lack ofhomogeneity, the highly porous composition and the relatively thin cellwall structure of envelope coke. The thin wall structure and highporosity of envelope coke is more apparent from inspection of FIGURE2(B) which was obtained at higher magnification.

Cauliflower coke, on the other hand, possesses a more homogeneoustexture and a generally higher density as evidenced by the smaller cellstructure and the relatively thick cell wall structure. The cauliflowerend of the coke, however, is highly fissured and cracked from the severethermal stresses introduced into this material during its formation.Gross cracks and fissures in the coke are evident from an inspection ofthe coke fragment in FIG- URE 2(A). Microscopic cracks are evident froman inspection of FIGURES 2(D) and 2(G). In addition, the weaknesses incauliflower coke appear to align themselves as indicated in FIGURE 2(H)by the general lineation from the point m to the point n. Along thislineation, an area of extremely thin wall structure indicatespotentially severe weaknesses and probable fracture of the materialunder mechanical shock.

The dense, good metallurgical coke which exists between the cauliflowerend and the envelope end of coke oven product is illustrated in FIGURES2(G) and 2(F) as having a relatively homogeneous texture, a high densityas indicated by relatively small cells and appreciable strength asindicated by the relatively thick cell walls. This is the dense, goodcoke which forms the overwhelming bulk of the coke oven productavailable for use as a metallurgical fuel. Thus the principal losseswhich occur in potentially realizable metallurgical fuel from byproductcoke ovens result from abrasion and shattering of the highly porous,friable envelope coke and of theVV highly fissured cauliflower coke. Thefine particles resulting from abrasion and shattering form the bulk ofthe socalled coke oven breeze which is not marketable as a premiummetallurgical fuel.

FIGURE 3 presents photographs of a typical calcined formcoke produced inaccordance with the present invention. FIGURE 3(A) is a photograph o-f apillow block formcoke briquet. Figure 3(B) is a photograph of a pillowblock formcoke briquet which has been split along a longitudinal plane.An inspection of the gross properties of the formcoke briquets andfragments illustrated in FIGURES 3(A) and 3(B) shows a strikingsimilarity to the dense, good metallurgical coke which has been shown inFIGURE 2(A) at (b). The formcoke possesses the lustery appearance whichis characteristic of the graphitization of good metallurgical coke. Froma microscopic view Ythe'formcoke cell structure resembles that of dense,goed metallurgical coke rather than either envelope coke or cauliflowercoke.

FIGURE 3(C) is a photomicrograph taken at 3 power magnification of anentire longitudinal plane of a thin section of a formcoke briquetprepared according to the present invention. FIGURES 3(D) and 3(E) arephotomicrographs taken at power magnification of thin sections o-f ourproduct formcoke taken along a longitudinal and a transverse plane of aformcoke briquet respectively. The relatively homogeneous character ofour product formcoke is apparent from inspection of FIGURES 3 (C) 3(D)and 3(E). The desirable properties manifested in FIGURES 3(C), 3(D) and3(E) include a homogeneous texture, a relatively thick cell wallstructure and an absence of fissures or lineations of weak cell walls.In addition, the absence of identifiable particles of the startingmaterials should be noted. The individual discrete starting materialshave merged into a continuum of carbonaceous material in which thestarting particles of material have lost their discrete identity.

Comparison of FIGURE 3(C) with FIGURES 2(B), 2(C) and 2(D) (all taken at3 power magnification) would indicate that the formcoke of FIGURE 3( C)possesses a generally different texture and structure than any portionof the metallurgical coke fragments. However, comparison of our formcokein FIGURES 3 (D) and 3 (E) with metallurgical coke in FIGURES 2(E),2(F), 2(G) and 2(H) (all taken at l5 power magnification) shows thesimilarity which exists between our formcoke and the dense, strongmetallurgical coke FIGURE 2(F). While the individual cells of ourformcoke appear to be generally smaller than the individual cells of thedense, strong coke, nevertheless, the formcoke cell Walls are equallythick and strong in appearance. Moreover, the fact that the bulk densityof our formcoke compares with the bulk density of good, strongmetallurgical coke indicates that the fractional void space of ourformcoke is about the same as the fractional void space of goodmetallurgical coke.

FIGURE 4 presents a photomicrographic comparison of thin sections of lowstrength metallurgical coke, high strength metallurgical coke andformcoke prepared according to the present invention. A thin section oflow strength metallurgical coke (prepared from poorly coking coalblends) is presented in FIGURE 4(A) at 3 power magnification and inFIGURES 4(B) and 4(C) at l5 power magnification. A high strengthmetallurgical coke is presented in FIGURE 4(D) at 3 power magnificationand in FIGURES 4(B) and 4(F) at l5 power magnification. Formcokeaccording to the present invention is presented n FIGURE 4(G) at 3 powermagnification and in FIGURES 4(H) and 4(1) at 15 power magnification.

Microscopic cracks of the low strength metallurgical coke are apparentin the photomicrograph in FIGURE 4(A).V The highly porous nature of thelow strength metallurgical coke is apparent from inspection of FIG- URES4(A), 4(B) and 4(C). A general lineation of large cells joined by thincell walls can be detected in FIGURE 4(0) The high strengthmetallurgical coke illustrated in FIG- URES 4(B), 4(B) and 4(F)'has amore nearly homogeneous texture, has generally smaller cells with largercell wall structure and a less porous composition.

The formcoke of our invention much moreV nearly resembles the highstrength metallurgical coke than the low strength metallurgical coke.The l5 power photomicrographs of our formcoke in FIGURES 4(H) and 4(1)illustrates a porous composition, a homogeneous texture and a thick cellwall structure similar to that shown for the high strength metallurgicalcoke in FIGURES 4(E) and 4(F). While the individual cells of ourformcoke appearY to be generally smaller than those found in the highstrength metallurgical coke, nevertheless, the fractional void space inboth materials is about the same as evidence by the nearly identicalbulk densities of the two materials.

EXAMPLE I To illustrate the formcoke preparation of our invention, 331lbs. of briquet formulation was prepared as follows:

20.5 lbs. (6.2 wt. percent) of high carbon pitch.

17.5 lbs. (5.3 wt. percent) of low carbon pitch obtained from tarproduced by iiuidized low temperature carbonization of Montour coal, atypical high volatile caking coal from the Pittsburgh seam. The materialwas mixed as a crushed solid capable of passing through a 0.5 mm.screen.

16.5 lbs (5.'0 wt. percent) of recycle formcoke fragments crushed topass through a 3.0 mm. screen.

82.5 lbs (24.9 wt. percent) of Montour coal, a typical high volatilecaking coal from the Pittsburgh seam. The material was crushed to passthrough a 0.5 mm.

Y screen.

193.8 lbs. (58.6 wt. percent) of uidized LTC char prepared from Montourcoal at a carbonizing temperature of about 925 F.

The formulation was well mixed at 50-52 C., kneaded for about 8 minutesat 95 C. and briqueted in a roll press maintained at 92-96 C. The rawbriquets had a measured average point crushing strength of 30 kilogramswhen the briquet rolls were forced-fed, but only 24 kilograms when therolls were not forced-fed.

46.5 pounds of the raw briquets were selected by hand picking to insurethat only whole briquets were Vfurther treated. The briquets were shockheated in a hot oven tofabout 500 C. in less than 30 minutes andthereafter heated to about 930 C. in an additional 270 minutes. Thecalcined briquets were cooled and recovered.

The product formcoke had a Micum abrasion index of l 95.9%. Micumabrasion indices above about 90% are considered to represent excellentmetallurgical 5 coke. Values above Vabout are considered to representacceptable metallurgical coke. The porosity was 50.34%. The true densitywas 1.80. The volatile matter content was 1.3%.

29.3 pounds of coke was produced from the 46.5 pounds of startingbriquets. Only 1.9 pounds of the coked product was in the form ofparticles which would pass through a 10 mm. screen. 24.1 pounds of thecoke appeared intact in the uniform shape of the original briquets. 3.3pounds of the coke appeared as briquet fragments which were retained ona 10 mm. screen.

EXAMPLE II A briquet formulationwas prepared from low temperais" l turecarbonization char which was prepared in a rotating kiln (Disco process)instead of by a uidized process. The formulation was as follows:

5.3 weight percent of low carbon pitch obtained from tar produced byiiuidized low temperature carbonization of Montour coal, a typical highvolatile caking coal from the Pittsburgh seam.

6.2 weight percent of high carbon pitch.

5.0 weight percent of recycle formcoke fragments crushed to pass througha 3.0 mm. screen.

25.0 weight percent of Montour coal, a typical high Volatile caking coalfrom the Pittsburgh seam, crushed to pass through a 0.5 mm. screen. L

58.5 weight percent of crushed LTC char prepared by the Disco process ina rotating kiln at S50-900 F. The crushed char passed through an 8 meshTyler standard screen; 5.7 percent was retained on a 14 mesh Tylerstandard screen; 25.5 percent passed through a 325 mesh Tyler standardscreen.

Ten briquets (one-inch pillow blocks) were prepared at 100 C. under 5000p.s.i. pressure. The briquets were shock heated to 1l00 F. andthereafter calcined at 1800 F. for 30 minutes. The heating rate duringcalcining was 20 F. per minute. The resulting briquet product wasseverely cracked; not one briquet remained intact.

According to the provisions of the patent statutes, we have explainedthe principle, preferred construction, and mode of operation of ourinvention and have illustrated and described what we now consider torepresent its best embodiment. However, we desire to have it understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than as specically illustrated and described.

We claim:

l. A porous formcoke of substantially uniform size and shape obtained bythe coking of a composition having a volatile matter content in excessof 22 percent and containing to 35 percent by weight of a particulatebituminous caking coal, 80 to 45 percent by weight of a uidized lowtemperature carbonization char derived from bituminous coal, and 6 to 20percent by weight of pitch derived by pyrolysis of bituminous coal, saidformcoke having a substantially homogeneous carbonaceous continuum, aMicum abrasion index above 90 percent, an apparent density of 0.80 to0.95, a volatile matter content less than 2 percent and beingsubstantially free of discrete granular particles of the startingmaterials.

2. A composition for use as a raw material in the preparation offormcoke which comprises 10 to 35 percent by weight of a finely dividedcaking bituminous coal, 80 to 45 percent by weight of char having a bulkdensity less than 30 pounds per cubic foot and which has been producedby uidized low temperature carbonization of bituminous coal and 6 to 20percent by weight of pitch obtained by pyrolysis of bituminous coals andhaving a melting point (ring and ball) of 60 to 90 C. including at least1 to 12 percent by weight of a high carbon pitch which has a xed carboncontent exceeding 25 percent and up to percent by weight of a low carbonpitch which has a fixed carbon content less than percent, said coal,char and pitch being substantially homogeneously intermixed and having avolatile matter content, when intermixed, in excess of 22 percent.

3. The composition of claim 2 in which the high carbon pitch is aproduct of coal pyrolysis and has been heated to a temperature aboveabout 1500 F.

4. The composition of claim 2 in which the high carbon pitch is obtainedfrom the evolved hydrocarbonaceous vapors resulting from coking ofcompositions as dened in claim 2.

5. The composition of claim 2 in which the low carbon pitch is obtainedfrom the evolved hydrocarbonaceous vapors resulting from fluidized lowtemperature carbonization of high, volatile bituminous coal.

-6. *The* composition of claim 2 in whichV up to about 8` percent byweight of tinely divided fragments of calcined formcoke is homogeneouslyintermixed therewith.

7. A porous formcoke of substantially uniform size and shape obtained byshaping the composition of claim 2 and coking the shaped composition,said coking including the steps of shock heating the composition to atemperature above the plastic temperature of the coal, retaining theshaped composition at a temperature below about 1250 F. until the entirecomposition has attained a temperature above the plastic temperature ofthe coal and thereafter continuing to heat the resulting cokedcomposition to a calcining temperature.

8. The composition of claim 2 in which the char has not been heated to atemperature above 1350 F. and has has been produced by the uidized lowtemperature carbonization of high volatile bituminous coal.

9. A method for preparing formcoke comprising substantiallyhomogeneously intermixing 10 to 35 percent by weight of a finely dividedcaking bituminous coal, to 45 percent by weight of char having a bulkdensity less than 30 pounds per cubic foot which has not been exposed toa temperature above 1350 F. and which has been produced by fluidized lowtemperature carbonization of high volatile bituminous coal, 6 to 20percent by weight of pitch obtained by pyrolysis of bituminous coal andhaving a melting point (ring and ball) of 60 to 90 C. including at least1 to 12 parts by weight of a high carbon pitch obtained by pyrolysis ofbituminous coal which has a ixe-d carbon content exceeding 25 percentand up to 15 percent by weight of a low carbon pitch obtained bypyrolysis of bituminous coal which has a fixed carbon content less than20 percent, pressing a shaped briquet from the resulting mixture at atemperature slightly above the melting point of said pitches, coking thesaid shaped briquet by iirst shock heating to a temperature above theplastic temperature of the coal, retaining the briquet at a temperaturebelow about 1250 F. until the entire briquet has attained a temperatureabove the plastic temperature of the coal, and thereafter continuing toheat the resulting coked briquet to a calcining temperature.

l0. A method for preparing formcoke comprising substantiallyhomogeneously intermixing 10 to 35 percent by weight of a finely dividedcaking bituminous coal, 80 to 45 percent by weight of char, having abulk density less than 30 pounds per cubic foot which has not beenexposed to a temperature above 1350 F. and which has been produced byuidized low temperature carbonization of high volatile bituminous coal,6 to 20 percent by weight of pitch obtained by pyrolysis of bituminouscoal and having a melting point (ring and ball) of 60 to 90 C. includingat least 1 to 12 percent by weight of a high carbon pitch obtained bypyrolysis of bituminous coal which has a fixed carbon content exceeding25 percent and up to l5 percent by weight of a low carbon pitch obtainedby pyrolysis of bituminous coal which has a fixed carbon content lessthan 20 percent, pressing a shaped briquet from the resulting mixture ata temperature slightly above the melting point of said pitches, cokingthe said shaped briquet by first shock heating to a temperature abovethe plastic temperature of the coal, retaining the briquet at atemperature below about 1250 F. until the entire briquet has attained atemperature above the plastic temperature of the coal, thereaftercontinuing to heat the resulting coked briquet to a calciningtemperature above l550 F., recovering the resulting calcined briquet asproduct, recovering the evolved hydrocarbonaceous vapors resulting fromthe coking and calcining treatment, recovering from said evolvedhydrocarbon vapors the high carbon pitch for use as the said high carbonpitch.

l1. A method for preparing formcoke from high volatile caking coalcomprising subjecting a portion of high volatile caking coal to lowtemperature carbonization under fluidized conditions, recovering evolvedhydrocarbonaceous LTC vapors and particulate uidized LTC char i5 havinga bulk density less than 30 pounds per cubic foot, recovering low carbonpitch from said evolved hydrocarbonaceous LTC vapors, substantiallyhomogeneously intermixing a briquet formulation comprising 10 to 35percent by weight of nely divided high volatile caking coal, S0 to 45percent by weight of said iluidized LTC char, 6 to 20 percent by weightof pitch including at least 1 to 12 percent by Weight of a high carbonpitch and up to 15 percent by weight of said low carbon pitch, pressinga shaped briquet from the resulting mixture at a temperature slightlyabove the melting point of said pitch, coking the said shaped briquet byfirst shock heating to a temperature above the plastic temperature ofthe coal, re taining the briquet at a temperature below about 1250 F.until the entire briquet has attained a temperature above the plastictemperature of the coal, thereafter continuing to heat the resultingcoked briquet to a calcining temperature above 1550 F., recoveringevolved hydro` carbonaceous vapors from the coking and calcining treat'-Y ments, recovering high carbon pitch from said last-mentionedhydrocarbonaceous vapors for use as the high carbon pitch component insaid briquet formulation, and recovering a calcined coked briquet asproduct.

References Cited in the iile of this patent UNITED STATES PATENTS

11. A METHOD FOR PREPARING FORMCOKE FROM HIGH VOLATILE CAKING COALCOMPRISING SUBJECTING A PORTION OF HIGH VOLATILE CAKING COAL TO LOWTEMPERATURE CARBONIZATION UNDER FLUIDIZED CONDITIONS, RECOVERING EVOLVEDHYDROCARBONACEOUS LTC VAPORS AND PARTICULATE FLUIDIZED LTC CHAR HAVING ABULK DENSITY LESS THAN 30 POUNDS PER CUBIC FOOT, RECOVERING LOW CARBONPITCH FROM SAID EVOLVED HYDROCARBONACEOUS LTC VAPORS, SUBSTANTIALLYHOMOGENEOUSLY INTERMIXING A BRIQUET FORMULATION COMPRISING 10 TO 35PERCENT BY WEIGHT OF FINELY DIVIDED HIGH VOLATILE CAKING COAL, 80 TO 45PERCENT BY WEIGHT OF SAID FLUIDIZED LTC CHAR, 6 TO 20 PERCENT BY WEIGHTOF PITCH INCLUDING AT LEAST 1 TO 12 PERCENT BY WEIGHT OF A HIGH CARBONPITCH AND UP TO 15 PERCENT BY WEIGHT OF SAID LOW CARBON PITCH, PRESSINGA SHAPED BRIQUET FROM THE RESULTING MIXTURE AT A TEMPERATURE SLIGHTLYABOVE THE MELTING POINT OF SAID PITCH, COKING THE SAID SHAPED BRIQUET BYFIRST SHOCK HEATING TO A TEMPERATURE ABOVE THE PLASTIC TEMPERATURE OFTHE COAL, RETAINING THE BRIQUET AT A TEMPERATURE BELOW ABOUT 1250* F.UNTIL THE ENTIRE BRIQUET HAS ATTAINED A TEMPERATURE ABOVE THE PLASTICTEMPERATURE OF THE COAL, THEREAFTER CONTINUING TO HEAT THE RESULTINGCOKED BRIQUET TO A CALCINING TEMPERATURE ABOVE 1550*F., RECOVERINGEVOLVED HYDROCARBONACEOUS VAPORS FROM THE COKING AND CALCININGTREATMENTS, RECOVERING HIGH CARBON PITCH FROM SAID LAST-MENTIONEDHYDROCARBONACEOUS VAPORS FOR USE AS THE HIGH CARBON PITCH COMPONENT INSAID BRIQUET FORMULATION, AND RECOVERING A CALCINED COKED BRIQUET ASPRODUCT.